U.S. Pat. No. 4,649,144 discloses 7-(3-amino-1-pyrrolidinyl)-1-Cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-1,8-na phthyridine-3-carboxylic acid as having antibacterial activity. In the patent, it is recognized that there is an asymmetric carbon atom on the pyrrolidine ring of the compound and that the compound can exist in optically active forms. Nevertheless, the patent does not describe the synthesis of these optically active forms nor does it describe or suggest which, if any, of the optically active forms would have antibacterial activity equal, better or less than the racemic compound, the compound specifically described in the patent.
We have now found that the S form of 7-(3-amino-1-pyrrolidinyl)-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-1,8-na phthyridine-3-carboxylic acid has significantly better activity against both gram-positive and gram-negative bacteria in vitro as well as in vivo. The S isomer is surprisingly not only better than its opposite R isomer but also better than the racemic compound described in the above patent.